I'd be very surprised if it were accurate. There is no indication of the source of data or the method of collection (or at least none I can find), and the list of colours for which they offer "simulation" makes me think it's based on a pretty narrow database, possibly even one stone per colour.

Plus, from what I understand, it's not a price list, but a price simulator. You may or may not find a stone at the price or price range listed, and you are on your own locating it!!!

Ummm. It makes sense, but the problem is "how many"? And what's the volume? And the update frequency?

Plus - as I edited above - it's not a price list; it's a price simulator or price record of what diamonds went for (or was asked for them; beware of the difference!), so it's of limited use unless you trade regularly.